This invention relates to a proton-beam therapy linac, and more particularly to such a unit which is capable of offering high-level performance in an extremely compact and relatively low-cost form.
With respect to the disclosure and discussion which follow herein, several prior art documents are useful, and are referred to in the text. These references are herebelow listed in the order in which they are mentioned: (1) J. M. Sisteron. "Clinical Use of Protons and Ion Beams from a World-Wide Perspective," NIM B40/41, pp. 1350-1353, 1989; (2) J. M. Slater, "Developing a Clinical Proton Accelerator Facility; Consortium-Assisted Technology Transfer," Proceedings of this conference: (3) P. Mandrillon, "High Energy Medical Accelerators," EPAC-90 Proceedings, Nice, France, June 1990, pp. S4-S8; (4) G. Lawrence (Los Alamos National Lab), Oral Presentation, PTCOG-13, Berkeley, Calif., November 1990; and (5) M. Goitein, "Proton Beam Intensity," Report of the Facilities Working Group, PTCOG, September 1987.
Exploring the background of this invention, the use of electron linacs to great cancer has experienced an explosive growth during the past two decades or so, with more than six thousand accelerators (linacs) estimated now to be in use around the world. Although it is widely recognized that proton beams have major advantages over these photon and electron-beam machines, extensive use of proton beams has not been realized due to the lack of dedicated facilities. However, more than nine thousand patients have by today been treated worldwide with ion beams at institutions with physics research accelerators (see Reference Document 1). The success of these programs has led to significant interest within the medical community in dedicated proton treatment facilities. The first such system, a 250-MeV synchrotron at Loma Linda Medical Center in California, is now treating patients (see Reference Document 2). A full description of the construction and operation of this system is found in U.S. Pat. No. 4,870,287, issued to Cole et al. on Sep. 26, 1989 for MULTI-STATION PROTON BEAM THERAPY SYSTEM.
As is pointed out by Mandrillon (Reference Document 3), the key requirements for a proper, dedicated proton therapy accelerator are: (1) that is must be compact enough for installation in a large hospital; (2) that it must be highly reliable and easy to operate; (3) that it must be compatible with beam scanning and isocentric gantries; and (4) that it must have a maximum energy capability greater than 200-MeV, Mth an intensity sufficient to treat large tumors in short irradiation times. Other important considerations include safety, ease of maintenance, and costs (equipment, facility and operation).
While the synchrotron facility at Loma Linda appears to be technically viable, its cost and complexity have caused radiation therapy groups to consider alternative approaches.
Conventional protons linacs are routinely used for injecting beams into synchrotrons, but they are considered to be too expensive and too powerful for low-current, high-energy proton acceleration. However, a "proton version" of the conventional S-band (operating at frequencies around 3000-MHz) electron linacs used for radiation therapy, employed according to the preferred embodiment of the invention disclosed and described herein, satisfies all of the requirements for an appropriate, dedicated proton therapy accelerator. While cascaded linacs have previously been employed for accelerating protons, high-frequency structures (i.e. those operating at around 3000-MHz) have been considered only for accelerating electrons. It is possible, for example, to use side-coupled linac structure with an operating frequency near 3000-MHz (S-band), for this application due to the very low current required from the same. The use of multiple, side-coupled linac (SCL) tanks, and rf power amplifiers, allows for variable output energy. A compact, high-frequency drift-tube linac (DTL) having a stepped-frequency (dual, 1:2 frequency ratio herein) can be used, and is used in the present invention, as the injector to the SCL at 70-MeV, with a conventional radio-frequency-quadrupole (RFQ) linac functioning as the DTL's input. It is the cascaded organization and arrangement of such an SCL, stepped-frequency DTL and RFQ for the acceleration of low-peak-current proton beams (see Table 1 below) that forms the foundation of the system of the present invention.
Various other important features, objects and advantages which are offered by the linac of the present invention will become more fully apparent as the description That now follows is read in conjunction with the accompanying drawings.